Removal of alkali metals from inaccessible locations



3,044,869 REMOVAL OF ALKALI METALS FROM INACCESSIBLE LOCATIONS Louis .Silverman, Los Angeles, Calif., and Robert A.

Sallach, Ames, Iowa, assiguors to North American Aviation, Inc.

No Drawing. Filed Feb. 19, 1960, Ser. No. 9,673 7 Claims. (Cl. 75-66) Our invention relates to a method of removing alkali metals from inaccessible locations and more particularly to a method of removing hot molten sodium from inaccessible places without chemical destruction.

Alkali metals, and particularly sodium and sodiumpotassium (NaK) find application as industrial heat transfer agents and as 'coolants in nuclear reactors due to their excellent heat transfer characteristics and low vapor pressure. A difficulty in the use of such coolants is the problem of removal from a system which is shut down for reconstruction or repairs. In practice, such metals seek out low and inaccessible locations from which removal is diflicult.

One of the present methods of removing alkali metals is by suction, but when the metal cannot be reached by a suction pump, other methods are in order. When sodium, for example, has wet a surface, it may be removed by chemical destruction with water or alcohols. The reaction with water is highly energetic and frequently explosive. Sodium also reacts with most organics at temperatures above its melting point (97.5 C.). Such reaction is usually accompanied by the formation of explosive quantitles of hydrogen, and hydroxides, or alcoholates. With other organics formation of sodium alkyls, phenyls, naphthyls, etc. occurs, in which event very reactive, inflammable, or insoluble compounds are formed. Another serious disadvantage in chemical destruction of alkali metals by most organics or steam is the corrosive action of reaction products on the system.

An object of our present invention is to provide an improved method of removing alkali metals from an inaccessible location.

Another object is to provide a method of removing adherent alkali metal deposits from inaccessible zones without chemical destruction of the metal or damage to the system.

Another object is to displace sodium from contact with a metal surface which it has wet in an inaccessible location, and then to remove it therefrom.

Still another object is to displace sodium from contact with steel in an inaccessible zone with an inert organic medium and to cause the sodium to float on the medium for easy removal.

Other objects and advantages of our present invention will become apparent from the following description, taken together with the appended claims.

In accordance with our present invention, we have provided a method of removing at least one alkali metal selected from the group consisting of lithium, sodium, potassium, and NaK from an inaccessible location, which comprises contacting said metal with a partially hydrogenated polyphenyl containing 2 to 4 phenyl rings.

The use of our organic compounds for removing the above-named alkali metals from inaccessible areas has a number of advantages. The partially hydrogenated polyphenyl will remove the metal from adherent contact with a metal surface. For instance, it will de-wet a sodium deposit on stainless steel. Then, under the conditions discussed below, the sodium will rise and float on the partially hydrogenated polyphenyl, from where it may easily be removed from the system. Furthermore, our organic agents will not react with the alkali metals to form insoluble organic compounds, or form explosive or nited States Patent ice corrosive mixtures. Finally, our organic compositions are thermally stable at all temperatures required for alkali metal removal.

The organic compounds, which we have discovered to be unexpectedly satisfactory for removing the above alkali metals from inaccessible locations, are essentially at least one partially hydrogenated polyphenyl containing 2 to 4 phenyl rings, for example partially hydrogenated biphenyl, biphenylene, terphenyl ('ortho, meta, and para isomers) and quaterphenyl. The degree of hydrogenation or saturation of such polyphenyls may satisfactorily vary from about 35% to about 60%, while about 40-50% s optimum. Such partially hydrogenated polyphenyls are commercially available, for instance under such trade names as HB-40, an isomeric mixture of terphenyls. The isomeric terphenyl mixtures are cheaper and more readily available, and hence are preferred. Such isomeric terphenyl compositions melt in the range of about 0-10? C., and are easily supercooled, and do not begin to decompose until about 250 C.

Our alkali metal removal method is temperature dependent. The temperature should be above the melting point of the metal to remove any adherent deposits. The upper temperature limit is about 250 C. (the above-mentioned polyphenyl decomposition temperature); a temperature of about 225 C. is a useful upper limit to allow operating latitude. Thus, with lithium (M.P. 186 C.), the temperature may satisfactorily be about 190-225? C., and with potassium (M.P. 623 (3.), about -225 C., while about 65100 C. is optimum for potassium removal. NaK is a series of sodium-potassium alloys, the liquid species of which have a melting point range of about -10 to 30 C., depending upon the particular composition. The minimum temperature, then, must be above the melting point of the particular NaK alloy, with a maximum being about 150 C. for low content potassium; about 5060 C. is optimum for the removal of liquid NaK.

The removal of sodium is still more temperature dependent. We find that a minimum temperature of about 97.5 C. (M.P. of Na) is necessary to displace any sodium which has frozen out on metal surfaces. At temperatures above about C., the sodium will melt without chemical reaction and float to the surface. However, at temperatures above about 160 C., sodium will settle to the bottom of the organic fluid. Thus, the specific range of operation of sodium flotation is between about 100 C. (necessary temperature to liquify sodium) and about 160 C., the point at which sodium will settle rather than float on the organic. We find that the optimum operation temperature within this range is about -140 C., which leaves an adequate safety factor for the routine operation of our process, particularly if it is conducted on a large scale.

The organic material may be contacted with the alkali metal, either with or without stirring, with satisfactory results. However, we find that the metals float very conveniently to the top of the organic fluid without stirring, and that with stirring, some homogenation and dissemination of metal through the entire medium occurs, which makes its complete removal somewhat more difficult.

The following examples are offered to illustrate our invention in greater detail:

Example I One experimental apparatus consists of a hollow, type 304 stainless steel cylinder, welded to a bottom plate of the same material. A rubber stopper is drilled to accom tall-form 200-ml. beaker with a 2-hole rubber stopper; 7

the outlet tube of the receiver is attached to a vacuum line.

Clean sodium (about 150 g.) is transferred to the nitrogen-flushed pot which is quickly stoppered and blanketed with nitrogen. The sodium in the pot is heated to 300 C. so as to permit the sodium to wet the metal. The liquid sodium is then cooled to 130 C. and 150 g. of 44% hydrogenated terphenyl are added. The mixture in the pot is allowed to remain quiescent at 130 C. for 20 minutes, and then suction is applied. All but a small amount of residual sodium is removed with the organic material. This residual, which cannot be pumped or suctioned off, is then removed with a subsequent treatment as above. Any trace amounts of sodium or any sodium dross remaining after the vessel is opened may be treated with butyl alcohol, which mixes with the organic material and destroys the sodium metal or dross. The butylate dissolves in excess butyl alcohol.

Example II The procedure of ExampleI is followed except that the organic material is 35% hydrogenated biphenyl, and the operating temperature is 140 C. Virtually complete sodium removal is obtained in the first batch, and a second treatment completes the removal.

V Example -III The procedure of Example I followed except that the organic material is 60% hydrogenated terphenyl and' the operating temperature is about 115 C. Virtually complete sodium removal is achieved in two treatm'ents.

- ExampleIV- I i The procedure ofExampleII is followed except thatthe alkali metal is lithium and the operating temperature is 210 C. Virtually complete lithium removal is obtained.

Example 1V invention should be understood to be limited only as is indicated in the appended claims.

Having thus described our invention, we claim:

1. A process 'for removing at least one alkali metal selected from the group consisting of lithium, sodium, NaK, and potassium from a first zone to a second zone remote from said first zone, comprising contacting said metal with a partially hydrogenated polyphenyl containing 2 to 4 phenyl rings, which polyphenyl is at a temperature between the melting point of said metal and 250 C., floating said metal on said polyphenyl, and removing said metal and said polyphenyl from said first zone to said second zone.

2. The method of claim 1 wherein said about 35 to hydrogenated.

3. A process for removing sodium from a first zone to a second zone remote from said first zone, comprising contacting said sodium with a partially hydrogenated polyphenyl containing 2 to 4 phenyl rings, which polyphenyl is at a temperature between about C. and about 160 polyphenyl is C., floating said sodium on said polyphenyl, and removing said sodium and said polyphenyl from said first zone to said second zone.

4. The method of claim 3 wherein the about -140 C. v

5. The method of claim 3 whereinsaid polyphenyl is about 35 to-60% hydrogenated.

' 6. A process for removing sodium from a first zone to a second zone remote from said first zone, comprising temperature is contacting said sodium with a partially hydrogenated terphenyl, which terphenyl is at a temperature between about 100 C. and C., floating said sodium on said terphenyl, and removing said sodium and said terphenyl from said first zone to said second zone.

7. The method of claim 6 wherein said terphenyl is about 40 to 50% hydrogenated, and said temperature is about 120-140 C.

References Cited in the file of this patent York, 1938, pages 368 and 369 relied on. 

1. A PROCES FOR REMOVING AT LEAST ONE ALKALI METAL SELECTED FROM THE GROUP CONSISTING OF LITHIUM, SODIUM, NAK, AND POTASSIUM FROM A FIRST ZONE TO A SECOND ZONE REMOTE FROM SAID FIRST ZONE, COMPRISING CONTACTING SAID METAL WITH A PARTIALLY HYDROGENATED POLYPHENYL CONTAINING 2 TO 4 PHENYL RINGS, WHICH POLYPHENYL IS A T A TEMPERATURE BETWEEN THE MELTING POINT OF SAID METAL AND 250* C., FLOATING SAID METAL ON SAID POLYPHENYL, AND REMOVING SAID METAL AND SAID POLYPHENYL FROM SAID FIRST ZONE TO SAID SECOND ZONE. 